1. Field of the Invention
The invention is drawn to novel biocontrol agents for control of Fusarium head blight.
2. Description of the Prior Art
Fusarium head blight (FHB) is a devastating disease of wheat and barley throughout the semi-humid and humid cereal producing regions of the world (McMullen et al., 1997, Scab of wheat and barley: are emerging disease of devastating impact. Plant Disease, 81, 1340-1348; Muthomi et al., 2002, Susceptibility of Kenyan wheat varieties to head blight, fungal invasion and deoxynivalenol accumulation inoculated with Fusarium graminearum, Journal of Phytopathology, 150, 30-36; Yu. Gagkaeva and Yli-Mattila, 2004, Genetic diversity of Fusarium graminearum in Europe and Asia, European Journal of Plant Pathology, 110, 551-562). FHB is caused primarily by Fusarium graminearum Schwabe Group 2 (Aoki and O'Donnell, 1999, Morphological and molecular characterization of Fusarium pseudograminearum sp. nov., formerly recognized as the Group 1 population of F. graminearum, Mycologia, 91, 597-609) [perfect state=Gibberella zeae (Schwein.) Fetch]. In addition to causing grain yield loss, G. zeae can produce mycotoxins such as the estrogenic toxin zearalenone (F-2) (Hesseltine et al., 1978, Fungi, especially Gibberella zeae, and zearalenone occurrence in wheat. Mycologia, 70, 14-18) and the trichothecene deoxynivalenol (DON, vomitoxin) (Snijders, 1990, Fusarium head blight and mycotoxin contamination of wheat, a review. Netherlands Journal of Plant Pathology, 96, 187-198) that can have a deleterious effect on grain quality [Cardwell et al., 2001, Mycotoxins: the cost of achieving food security and food quality, APS Net: Feature story August, 2001] and animal health [Marasas, 1991, Toxigenic Fusaria, in: Mycotoxins and Animal Foods, J. E. Smith and R. S. Henderson, eds., CRC Press, Inc., Boca Raton, Fla.; Beardall and Miller, 1994, Diseases in humans with mycotoxins as possible causes, in Mycotoxins in Grain: Compounds Other than Aflatoxin (MILLER, J. D. & TRENHOLM, H. L., Eds.). Eagan Press, St. Paul, Minn., pp. 387-39; Pestka and Bondy, 1994, Immunotoxic effects of mycotoxins, in Mycotoxins in Grain: Compounds Other than Aflatoxin (MILLER, J. D. & TRENHOLM, H. L., Eds.) Eagan Press, St. Paul, Minn., pp. 339-358].
Reducing the impact of FHB on grain production and quality remains an intractable problem. Fungicides sometimes have reduced FHB [Wilcoxson, 1996, Fungicides for control of Fusarium head blight, Int. J. Tropical Plant Disease, 14, 27-50; Suty and Mauler-Machnik, 1997, Fusarium ear blight on wheat-epidemiology and control of Gibberella zeae, the teleomorph of Fusarium graminearum with Folicur, in Diagnosis and Identification of Plant Pathogens, Proceedings of the 4th International Symposium of the European Foundation for Plant Pathology (DEHNE, H. W., ADAM, G., DIEKMANN, M., FRAHM, J., MAULER-MACHNIK & VAN HALTEREN, P., Eds). Kluwer Academic Publishers, Dordrecht., pp. 243-246; Jones, 1999, Seedling blight development and control in spring wheat damaged by Fusarium graminearum Group 2. Plant Disease, 83, 1013-1018], but residues, reports of fungicide resistance and instances of DON content increases in grain can be concerns with their use [Mauler-Machnik and Zahn, 1994, Ear fusarioses in wheat-new findings on their epidemiology and control with Folicur (tebuconazole). Pflanzenschutz-Nachrichten Bayer, 47, 129-155; Ramirez et al., 2004, Impact of environmental factors and fungicides on growth and deoxynivalenol production by Fusarium graminearum isolates from Argentinian wheat. Crop Protection, 23, 117-125; Chen et al, 2000, Recent advances in wheat head scab research in China, in Proc. Int. Symp. Wheat Improvement for Scab Resistance (RAUPP, W. J., MA, Z., CHEN, P. & LIU, D., Eds.). Nanjing Agricultural University, Jiangsu, China, pp. 258-273; Gale et al, 2002, Population analysis of Fusarium graminearum from wheat fields in eastern China, Phytopathology, 92, 1315-1322]. Although the development of resistant cultivars or anatomically altered varieties (Legzdina and Buerstmayr, 2004, Comparison of infection with Fusarium head blight and accumulation of mycotoxins in grain of hulless and covered barley, Journal of Cereal Science, 40, 61-67) of small grains holds promise in reducing FHB, highly resistant cultivars with ideal agronomic traits have not been developed (Johnston, 1994; Bushnell et al., 1998, Genetic engineering of disease resistance in cereals, Canadian Journal of Plant Pathology, 20, 137-149; Bai et al., 2000, Inheritance of resistance to Fusarium graminearum in wheat, Theoretical and Applied Genetics, 100, 1-8). The genetic diversity of G. zeae [O'Donnell et al., 2004, Genealogical concordance between the mating type locus and seven other nuclear genes supports formal recognition of nine phylogenetically distinct species within the Fusarium graminearium Glade, Fungal Genetics and Biology, 41, 600-623; McCallum et al., 2004, Barrage zone formation between vegetatively incompatible Fusarium graminearum (Gibberella zeae) isolates. Phytopathology, 94, 432-437; Walker et al., 2001, Variation among isolates of Fusarium graminearum associated with Fusarium head blight in North Carolina, Plant Disease, 85, 404-410; Cumagun et al., 2004, Genetic mapping of pathogenicity and aggressiveness of Gibberella zeae (Fusarium graminearum) toward wheat, Phytopathology, 94, 520-526] raises concerns regarding how durable the efficacy of fungicides and resistant cultivars will be. Conventional tillage of fields is partially effective in reducing pathogen inoculum production and, concomitantly, FHB (Miller et al., 1998, Effect of tillage practice on Fusarium head blight of wheat, Canadian Journal of Plant Pathology, 20, 95-103; Dill-Macky and Jones, 2000, The effect of previous crop residues and tillage on Fusarium head blight of wheat, Plant Disease, 84, 71-76; Pereyra et al., 2004, Survival and inoculum production of Gibberella zeae in wheat residue, Plant Disease, 88, 724-730), but minimum tillage is the preferred agricultural practice for soil conservation. Considering the potential of long distance inoculum dispersal and the diverse crops that can act as alternative hosts of the pathogen (Chongo et al., 2001, Reaction of seedling roots of 14 crop species to Fusarium graminearum from wheat head, Canadian Journal of Plant Pathology, 23, 132-137), crop rotation is an untenable solution.
Biological control of FHB has attracted considerable interest since the mid 1990's, and significant advances have been achieved [Perondi et al., 1996, Controle microbiologico da giberela do trigo, Fitopatologia Brasiliera, 21, 243-249; Bujold et al., 2001, Effect of Microsphaeropsis sp. on the production of perithecia and ascospores of Gibbereila zeae, Plant Disease, 85, 977-984; Schisler et al., 2002, Biological control of Fusarium head blight of wheat and deoxynivalenol levels in grain via use of microbial antagonists, in Mycotoxins and Food Safety (DeVRIES, J. W., TRUCKSESS, M. W. & JACKSON, L. S., Eds.). Kluwer Academic/Plenum Publishers, New York, pp. 53-69; da Luz et al, 2003, Biological control of Fusarium graminearum, in Fusarium head blight of wheat and barley (LEONARD, K. J. & BUSHNELL, W. R., Eds.) APS Press, St. Paul, Minn., 381-394; Gilbert & Fernando. 2004, Epidemiology and biological control of Gibberella zeae (anamorph Fusarium graminearum). Canadian Journal of Plant Pathology, 26, 1-9]. Public acceptance, compatibility with other disease management measures, and durability are all favorable factors in support of developing strategies for biologically controlling FHB.
Schisler et al. (U.S. Pat. No. 6,562,337) described the isolation of four yeast and one bacterium which were superior antagonists capable of suppressing FHB. These microorganisms, which were obtained from the anthers of wheat, included the yeast Cryptococcus flavescens OH 182.9 (originally classified as C. nodaensis) which was deposited in the Agricultural Research Service Culture Collection (NRRL) under deposit accession no. NRRL Y-30216. Recently, Schisler et al. (2006, Selection and evaluation of the potential of choline-metabolizing microbial strains to reduce Fusarium head blight, Biological Control, 39, 497-506) disclosed selecting choline-utilizing strains of microorganisms as biological control agents against FHB.
Although efforts for developing biological control agents for FHB have been effective, the development and use of chemical fungicides remain a valuable tool in the arsenal of agents for the reduction of FHB in cereals. Most recently the fungicidal chemical prothioconazole has received an exemption status for use on wheat at flowering for the reduction of FHB.
However, despite these and other advances, the need remains for improved microorganisms for use in the biological control of FHB.